i8 



BEGINNERS' ZOOLOGY 



surface of the sponge rough or smooth? Do any of the skeletal 

 spicules show on the surface? (Fig. 21.) Does the sponge thin 

 out near its edge? 



The egg of this sponge is shown in Fig. 23. It escapes from 

 the parent sponge through the osculum, or large outlet. As in 



most sponges, the first 

 stage after the egg 



ciliated and 



is 

 free-swim- 



ming. 



Fig. 23. — Eggs and spicules of fresh-water 

 sponge (enlarged). 



Marine Sponges. — 

 The grantia (Fig. 24) is 

 one of the simplest of 

 marine sponges. What is the shape of grantia? What is its length 

 and diameter? How does the free end differ from the fixed end? 

 Are the spicules projecting from its body few or many? 

 Where is the osculum, or large outlet? With what 

 is this surrounded ? The osculum opens from a central 

 cavity called the cloaca. The canals from the pores 

 lead to the cloaca. 



Buds are sometimes seen growing out from the 

 sponge near its base. These are young sponges formed 

 asexually. Later they become detached from the 

 parent sponge. 



Commercial " Sponge." — What part of the complete 

 animal remains in the bath sponge? Slow growing 

 sponges grow more at the top and form tall, simple, 

 tubular or vase-like animals. Fast growing sponges 

 grow on all sides at once and form a complicated system of canals, 

 pores, and oscula. Which of these habits of growth do you think 

 belonged to the bath sponge ? Is there a large 

 hole in the base of your specimen ? If so, this 

 is because the cloaca was reached in trimming 

 the lower part where it was attached to a rock. 

 Test the elasticity of the sponge when dry and 

 when wet by squeezing it. Is it softer when wet 

 or dry? Is it more elastic when wet or dry? 

 Fig. 25.— Plan of How man y oseula does your specimen have? 

 a sponge. How many inhalent pores to a square inch? 



Fio. 24.— 



Grantia. 



